The present invention relates to a network communication system, and more particularly, to a method and apparatus for overload control of a composite multimedia signal transmitted across one or more heterogeneous networks consisting of a hybrid switch device, including an ATM network, as separately switched monomedia streams.
The use of broadband networks, such as asynchronous transfer mode (ATM) networks, for the transfer of multimedia information, such as video, voice and data, has become increasingly popular due to the high data rate and flexibility associated with such networks. ATM networks, for example, utilize a cell-oriented switching and multiplexing technique, and are based upon the use of fixed-length xe2x80x9ccellsxe2x80x9d. ATM and other broadband networks have been embraced by the computer and telecommunication industries for networking existing and future multimedia applications, such as video conferencing, video-on-demand, and telephone applications.
Currently, multimedia information may be transmitted across ATM and other networks to an end user by means of an integrated transport protocol, whereby the various monomedia components within the composite multimedia signal are encoded and transported together. This integrated transport approach, however, imposes several limitations, which, if overcome, could greatly expand the flexibility and quality of multimedia communications, particularly across heterogeneous networks. For example, it is not expected that all end-user devices and network service subscribers on heterogeneous networks would desire, or be capable of accessing, all monomedia components in a multimedia presentation. For example, in a conference call, some end users may desire to access only voice and data, or just voice, and not video.
In addition, in the end-to-end path of multimedia sessions, heterogeneous network technologies, such as switches with different switch fabrics or diverse transport links, hereinafter referred to as xe2x80x9cnetwork segments,xe2x80x9d may be involved. For subscribers and locations where switch fabrics supporting a multimedia session are not available, only a subset of monomedia elements of a multimedia session may be supported. For example, if one or more network segments are wireless, the radio access (or the wireline portion of the wireless network) may only support voice, and not support data or video.
U.S. patent application Ser. No. 08/936,386, filed Sep. 25, 1997 and entitled xe2x80x9cMethod and Apparatus for Transporting Multimedia Information Over Heterogeneous Wide Area Networks,xe2x80x9d discloses a method and apparatus for separately transporting each monomedia stream, such as video, voice and data, of a composite multimedia signal across heterogeneous networks, including an ATM network. Thus, monomedia traffic from a multimedia session is transported over different network segments to different end users, which may or may not support or desire all multimedia components.
When a call is established in a monomedia or multimedia system, the call processor must perform call admission to ensure that sufficient switching resources are available in the system to handle the call. If the call processor is in an xe2x80x9coverloadxe2x80x9d condition, where the volume of signaling traffic exceeds the capacity of the call processor, the call processor should exercise overload control. If overload is not properly controlled, system throughput can be reduced, and even cause the network to cease operation. Although overload control problems can occur in both monomedia and multimedia networks, the issue is more critical for the multimedia system disclosed in U.S. patent application Ser. No. 08/936,386 U.S. Pat. No. 6,253,207, because each multimedia session requires a separate connection for each monomedia component. It is possible, however, that sufficient resources are available in the multimedia system for only a portion of the multimedia session. Under these circumstances, and depending on the requirements of the end user, the multimedia session may be rejected altogether, or the network may negotiate with the end user to establish one of the monomedia connections composing the multimedia session for which resources are available.
Several methods of overload control to maximize system throughput have been proposed or suggested for monomedia systems in order to maximize system throughput. These methods are primarily based on throttling signaling traffic before the signaling traffic enters the call processor. Throttling traffic can be performed in a number of ways, including (i) accepting or rejecting an arriving call or message with a predefined probability; and (ii) devising a xe2x80x9cgap,xe2x80x9d whereby the number of calls exceeding a threshold in a predefined time interval are rejected. These methods of overload control attempt to maximize the amount of time for which the call processor can perform xe2x80x9cuseful work.xe2x80x9d Useful work is defined as the rate of calls or messages that complete their functions within a predefined timer interval or with other desirable characteristics of the switching system.
As apparent from the above-described deficiencies with conventional systems for transporting multimedia information, a need exists for an improved method and apparatus for overload control in a hybrid switching system supporting multimedia communications that separately transports each monomedia stream of a composite multimedia signal across a network. A further need exists for a multimedia communication system that throttles individual monomedia components of a multimedia session in desired amounts. Yet another need exists for a multimedia communication system that determines whether to accept or reject a multimedia call when there is insufficient capacity for each monomedia component in the multimedia session.
Generally, according to one aspect of the present invention, a system for overload control is disclosed for hybrid switching systems consisting of multiple switch fabrics and one or more call processors that separately transport each monomedia stream, such as video, voice and data, of a composite multimedia signal. The overload control is based on the time delay for completion of call establishment of each multimedia session in the switching system. A rate-based method is utilized for determining the number of call requests that can be admitted into a network node in a given time interval.
When the average time delay for completion of call establishment of each multimedia session is below a predefined threshold, the hybrid switching system has sufficient capacity and an overload condition is not present and corrective measures are not required. According to an aspect of the invention, when the average time delay for completion of call establishment of each multimedia session, or a connection for any individual monomedia component within the multimedia session, exceeds a predefined threshold, the switching system is approaching an overload condition, and overload control techniques must be implemented to reduce the number of calls accepted in future time intervals. A decision is made at the beginning of each time interval based on the average call establishment time delay over some predefined period of time, to accept a determined number of calls during the time interval. Thus, the present invention adapts to the processing speed of the call processor and the available capacity of the switching system.
The number of calls, Kin, of each monomedia type, i, that can be admitted into a network node are determined for each time interval, T. The size of the interval, T, can vary, depending on the system requirements. In one preferred implementation, the number of calls, Kin, of each monomedia type, i, admitted into a network node for the n-th time interval, T, is based on the number of calls already admitted over the previous interval, Ninxe2x88x921.